A sucker rod is a rigid rod used in the oil industry to join together the surface and downhole components of a reciprocating piston pump installed in an oil well. These rods are typically between 25 and 30 feet (7 to 9 meters) in length, and threaded at both ends.
Certain methods of remanufacturing sucker rods for re-use comprise eliminating or reducing the fatigue stress in the used rods by a method involving thermally treating the rods at a temperature between about 200° C. and about 650° C. for 15 to 30 minutes. Typically this consists of normalization, upgrading or tempering, with reference to the material or rods remanufactured. After thermal treatment the rods are straightened while still hot to achieve the required straightness. Additionally, straightening while still hot allows for the removal of stress which can occur otherwise during the course of the straightening procedure.
Other methods used in the remanufacturing of rods such as sucker rods comprise the use of a device with two heads that have the ability to clamp two ends of the rod in need of treatment or modification. In this methodology, typically one head turns uncontrollably with the rod treated along its longitudinal central line. However, use of the aforementioned device can result in deformation of standard length sucker rods due to tension and torsion, even though cold working the rod's surface would improve the fatigue strength and the efficiency.
Typically the main process of reclaiming or reconditioning a used rod utilized in oil pump wells comprises obtaining the rod, cleaning the rod to remove contaminates from use in oil extraction, performing an inspection of the rod to determine if the rod should be reconditioned or discarded, categorizing the rod into steel class, heating the rod until plastic deformation, shaping the rod, cooling the rod and cutting the rod into the desired length. Embodiments of the invention pertain to a method for reconditioning a used sucker rod having a given diameter.
Typically, on pre-cleaned rods are found contaminates such as paraffin. Further, the cleaning process wherein contaminates are removed often comprises washing the rod with an organic compound. One organic compound typically used is kerosene. Other chemicals known in the art that are useful for cleaning rods are chemicals such as naptha and caustic acid. However, all of these aforementioned methods of cleaning leave toxic or caustic residue as a byproduct of the cleaning process.
Additionally, such cleaning agents may render chemicals attached to the rods soluble in organic compounds or in caustic acids. Such chemicals may themselves be toxic to the environment or pose cleanup problems at the cleaning facility.
It would therefore be advantageous to reduce the contamination to the environment and to the cleaning facility by the utilization of non-toxic cleaners and cleaners which do not result in solubility of contaminates from rods such as sucker rods. One such cleaning material is dry ice.
Cleaning via dry ice blasting is analogous to pressure washing, or sandblasting, since there is a media being moved at high speed, under pressure, to clean a specific target surface. However as compared to wet aqueous cleaning materials, dry ice is dry, thereby reducing or eliminating the short circuiting of electrical equipment or rusting bearings. Further, it is non-conductive, so it can even be used on or near energized circuits. Dry ice is also non-abrasive. Further, dry ice is attractive as a contaminant cleaner as dry ice causes no environmental harm. Rather, dry ice is a “food grade” product, meaning it can be used in food manufacturing, food preparation facilities and is FDA approved.
Because there is no secondary waste stream, dry ice blasting is advantageous from a cleaning standpoint. Typically, the only waste to clean up afterward is the grime, paraffin, rust or whatever contaminant was removed. Likewise, in the restoration applications total job time is greatly reduced due to the fact there is very little post-blast cleanup required.
There are several mechanical processes happening when dry ice particles strike a surface. Depending on the type of blasting system being used, and the air pressure and nozzle selected, the ice particles travel at speeds between 600 and 800 feet per second. Upon impact they sublimate into carbon dioxide gas. There is an expansion factor of 8× as this happens, so assuming the particles are able to initially penetrate the contaminant, this expansion occurs at the underlying substrate, thus lifting the contaminant off. There is also a thermal shock effect, as the particles are at sub-zero temperatures (−109.3 F).
Dry ice impacting a sucker rod or other pump rod surface with contaminants typically removes contaminates in one of three ways: via kinetic energy, via thermal shock or via a thermal-kinetic effect. Kinetic energy transfers the accelerated dry ice pellet as it hits the surface of the rod to be cleaned during the dry ice blasting process. The dry ice pellets sublimate upon impact. Likewise, thermal shock occurs when dry ice pellets strike a much warmer contaminated surface during the dry ice blasting. The cold temperature of the dry ice causes the bond between the surface being cleaned and the contaminants to weaken. This effect aids in the release of the contaminant when struck by the dry ice pellets during dry ice blasting. The thermal-kinetic effect combines the impact of sublimation and the rapid heat transfer discussed above. When the dry ice pellet hits the contaminated surface, the vapor expands fast enough that micro-explosions occur which take off the contaminants from the rod.